INDICATORS OF RESISTANCE OF SUNFLOWER PLANT TO BASAL STALK ROT (SCLEROTINIA-SCLEROTIORUM) - SYMPTOMATOLOGICAL, BIOCHEMICAL, ANATOMICAL, AND MORPHOLOGICAL CHARACTERS OF THE HOST

The object of this work was a study of the relationship between the field reactions of different sunflower genotypes to basal stalk rot (in terms of severe (dead plants) and incipient wilting, and lesion length) and some biochemical (phenol concentration), morphological (plant height, and stem and flower-bud diameters) and anatomical (xylem and cortical indexes) characters of the host. Plants from 8 inbred lines at closed flower-bud stage were artificially inoculated with mycelium at the base of the stem. The percentage of dead plants for each inbred line and the lesion length and wilting range for individual plants after 7 days were recorded. A positive and highly significant correlation coefficient between the percentage of dead plants and lesion length was found for the three years of the study (r = 0.83; P < 0.01). A highly significant association between lesion length and wilting range for individual plants was always found (P = 0.00). Postinfectional phenol content exhibited a strong negative correlation with lesion length and the percentage of dead plants in all the experiments (P = 0.05). Association between postinfectional phenol content and wilting range for individual plants was significant for all the years studied (P < 0.05). No correlation between phenol levels in healthy plants of the different sunflower genotypes and their susceptibility was found. Morphological characters positively correlated with lesion length but only plant height exhibited significant values for the three years. Associations between wilting range and morphological characters for individual plants were significant for one of the two years analyzed (P < 0.05). Xylem index showed a negative correlation with lesion length which was significant one of the two years studied. The lesion length measure seems to be a simple and direct method for resistance screening before the flowering period. Although strong relations with postinfectional phenol levels were found, their determinations would be too much time consuming and not completely reliable. The relationships between other characters measured and disease resistance would indicate that physiological mechanisms could be related to resistance.